The invention relates to an apparatus for producing video disks more particularly in accordance with a technique for molding a flexible substrate on a matrix carrying information in the form of microreliefs.
Optically readable video disks are generally such that the information is recorded along a spiral or concentric circle track, formed from a succession of elements whose dimensions are of the order of a micron: channels or projections according to the process. Microchannels are obtained for example by thermal ablation.
For certain applications, it may be useful to have available a more or less large number of identical copies obtained from the same original disk: either a specially etched matrix which will only serve for duplicating, or a disk capable of being recorded and read by the user.
Numerous copying processes are already known, particularly those using pressing techniques, such as those used for audio disks, which require the use for the copies of a thermo-deformable plastic material. The pressing processes well-adapted to large-scale production require heavy, cumbersome and expensive apparatus which is scarcely advantageous for small-scale production and cannot be used by the user himself.
More adapted to small-scale production are the molding processes consisting in contacting a matrix and a substrate with at least one intermediate molding agent. The apparatus is then lighter, simpler to use and inexpensive, able to be installed in any premises, such as a reprography apparatus for example, in the very place of use. Furthermore, molding does not generate mechanical stresses at the level of the relief impression and ensures a greater fidelity of reproduction than pressing. One of the problems met with is that of the inclusion of air bubbles between the matrix and the substrate. A process for molding flexible disks (floppy or semi-rigid) is described in French patent application No. 78 07 293 filed on Mar. 14, 1978 and published under the No. 2 384 404, according to which a photopolymerizable resin is deposited in a ring close to the center of the matrix, the flexible substrate is curved and applied against the resin then is progressively flattened against the matrix while driving the resin towards the periphery and avoiding the formation of air bubbles. The resin, which forms a layer of uniform thickness between the substrate and the matrix, is photopolymerized by ultraviolet radiation through the substrate and adheres then to the substrate and not to the matrix. The means for implementing this process, described in this application, comprise in particular a vacuum pump connection, so as to cause the substrate to be curved by application of a depression. To allow the substrate to be applied against the matrix, the depression is discontinued so that the substrate relaxes and is flattened on the matrix. The implementation thus described is delicate. The pressure exerted by the substrate on the matrix, with the ring of resin as intermediary, is not controlled and it is not easily maintained uniform and progressive. On the other hand, no means are provided for forming the central hole, perfectly positioned with respect to the annular recorded area.